The present application relates to the illuminating arts. It finds particular application in providing reliable and accurate dimming of a lamp associated with an inverter ballast and will be described with particular reference thereto. It is to be appreciated that the present dimmer can also provide dimming functionality to other lighting applications and is not limited to the above-referenced application.
In existing frequency dimming ballasts, conventional methods of dimming continuously change the frequency of oscillation to control the amount of current flowing through an arc, and therefore the lumen output of the lamp. This can result in the production of unwanted heat in the lamp drive coil. Additionally, high frequency interfaces can be complex and difficult to implement. Optical interfaces have also been tried with limited success, but are more costly and complex.
In a variable voltage system, the user risks electrical shock unless the interface is electronically isolated from the ballast. In a system that is referenced to a 277 Volt power supply, it would be hazardous to interact with any of the leads unless they were electrically isolated. Previous systems use relatively complicated schemes to monitor a signal across the primary winding of a transformer, pass it through the transformer, then demodulate it. Such a system is complicated and rather non-linear. This type of system also lacks the type of precision desired in a lamp dimmer.
The present application provides a new and improved dimming circuit for an electronic lamp ballast that overcomes the above-referenced problems and others.